This invention relates to multiwalled plastic containers which are comprised of an inner liner and outer structural wall supporting the liner. The liner material typically has barrier properties, (such as with respect to moisture, oxygen, carbon dioxide, etc.) which are far superior to the plastic material forming the outer structural container wall. The container liner may be of a single layer or of a multilayer design wherein each layer may be formed of a different material having a specific barrier property. Such containers are constructed of multiwalled or multilayer design since all of the desired barrier properties generally cannot be provided by one material.
Various techniques for molding hollow plastic articles and containers are known in the prior art. By one technique the multiwalled containers are produced by an injection-blow molding procedure. In producing containers by this procedure a previously thermoformed liner is positioned over a core rod in an injection-blow molding machine. The core rod is then positioned in the cavity of an injection molding zone and an injectable heated thermoplastic resin is injected into such cavity to form a composite preform or parison, wherein the liner comprises the inner wall portion thereof. The core rod with the composite preform thereon is removed from such injection mold cavity and is positioned next in the cavity of a blow molding zone. Fluid pressure is exerted on the preform between the preform and the core rod to an extent sufficient to make the preform expand into contact with adjacent wall portions defining the blow mold cavity which results in the production of a blown container. The blown container is removed from the blow mold cavity and the blown container is then separated from the core rod. Specific details relating an apparatus, materials, and techniques for producing such containers can be found in U.S. Pat. Nos. 4,162,883 and 4,309,380, both of which are granted to Donald G. Sauer and assigned National Can Corporation.
One possible problem with some prior art multiwalled containers, wherein the inner liner and the outer wall have an exposed edge at the container lip, is that a separation of the liner from the rim of the structural outer wall may possibly occur under certain circumstances. Such liner separation if it occurs can produce a less than desirable appearance and can present sanitation problems.
One cause of the liner separation problem is that the prior art injection molded or injection blow molded containers have a relatively small overlap between the lip of the liner and the outer wall rim region. Typically, the liner extends at most to the outer edge of the structural wall rim and terminates at the junction between the top rim surface and outer vertical surface, or side wall, of the outer wall. Another draw back in the design of the prior art containers is that the edge of the liner lip is exposed, thereby increasing the chance that the liner may be subjected to forces which can peel the liner away from the structural wall rim to create the aforementioned crevices. Moreover, the separation problem can be compounded by the fact that friction may be developed between the container closure and the inner liner overlap during the application or removal of the closure which can initiate or further propagate a separation. Also, in the case of prior art containers utilizing a multilayer liner a separation of the individual layers at the liner lip can occur resulting in additional crevices at which the container contents become trapped and present a further undesirable appearance.
Thus it can be appreciated that a need exists for injection molded and injection blow molded multiwalled containers having a liner sufficiently secured thereto in a manner which will eliminate or reduce the possibility of liner separation at the container rim.